1. Field of the Invention
The present invention relates to a zoom lens useful as a photographic optical system of an image pickup apparatus, such as a video camera, a digital still camera, a broadcast camera, or a silver-halide film camera.
2. Description of the Related Art
In recent years, an image pickup apparatus (camera) that uses a solid-state image sensor, such as a video camera or a digital still camera, has a large number of functions. Furthermore, the size of the entire apparatus is small at the same time. In addition, it is desired by the market that a photographic optical system used in such an image pickup apparatus has a high zoom ratio, is small in size, and is a zoom lens system having a relatively short total length (in the direction of front and back sides of the zoom lens system during shooting). If such a zoom lens is used, the thickness of a camera (the total front-to-back dimension of the camera during shooting) can be reduced.
Japanese Patent Application Laid-Open Nos. 2007-293051 and 2007-292795 each discuss a zoom lens having a reflection member (prism) for bending an optical path of a photographic optical system by 90 degrees in order to reduce the thickness of a camera.
When an operation for shooting an object is being performed, if vibration is applied to a zoom lens, then an image shake may occur. Accordingly, it is desired by the market that a zoom lens includes an image stabilization function for preventing or reducing an image shake. As such a zoom lens having an image stabilization function, a zoom lens has been used that corrects an image shake (hand shake) by moving a part of lens units constituting the zoom lens in a direction perpendicular to the optical axis. Hereinbelow, a “direction perpendicular to the optical axis” can also refer to a direction having a component perpendicular to the optical axis”.
As one type of the zoom lenses described above, U.S. Pat. No. 7,023,624 discusses a zoom lens including, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power and configured to correct an image shake by vibrating a part of lenses constituting the third lens unit in a direction perpendicular to the optical axis.
In the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051, in a five-unit zoom lens including, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power, a reflection member for bending the optical path is located on the image side of the second lens unit. Furthermore, the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051 executes zooming from the wide-angle end to the telephoto end by moving lens units so that the distance between the second and the third lens units becomes small. In addition, the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051 corrects an image shake by moving the entire third lens unit in a direction perpendicular to the optical axis.
In the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-292795, in a four-unit zoom lens including, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power, a reflection member for bending the optical path is located in each of the first and the third lens units. In the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-292795, the first and the third lens units are stationary while the second and the fourth lens units are movable during zooming. In addition, the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-292795 divides the third lens unit into two partial lens units and corrects an image shake by moving the partial lens unit on the object side in a direction perpendicular to the optical axis.
The zoom lens discussed in U.S. Pat. No. 7,023,624 divides the third lens unit into a first lens sub-unit having a positive refractive power and a second lens sub-unit having a positive refractive power. Moreover, the zoom lens discussed in U.S. Pat. No. 7,023,624 corrects an image shake by moving the second lens sub-unit on the image side in a direction perpendicular to the optical axis.
However, unless an optical member for executing the image stabilization function and a reflection member for bending the optical path are located at appropriate positions within the optical system, it may become difficult to acquire a high-quality image while achieving a small camera thickness when applied to a camera.
The zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051 corrects an image shake by displacing the entire third lens unit in a direction perpendicular to the optical axis. In the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051, the distance between the second and the third lens unit becomes smallest at the telephoto end, at which a large amount of image shake may occur. Accordingly, in the zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-293051, lens barrels that support respective lens units may easily interfere with each other. This interference of the lens barrels may become further serious when the zoom lens has a high zoom ratio.
The zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-292795 corrects an image shake by displacing a lens unit located close to the reflection member for bending the optical axis by 90 degrees in a direction perpendicular to the optical axis. Accordingly, lens barrels that support respective lens units may easily interfere with each other. In addition, it may become difficult to secure a sufficient amount of driving a correction lens unit for correcting an image shake.
In the zoom lens discussed in U.S. Pat. No. 7,023,624, no prism (reflection member) for bending the optical path is located on the optical axis. Accordingly, it becomes difficult to reduce the thickness of a camera. Furthermore, even if a prism is located within the optical system, it is difficult to achieve a high zoom ratio with the power arrangement discussed in U.S. Pat. No. 7,023,624.